Transformer encased in magnetic tape



Feb. 23 1965 B. M. GoLDsMrrH 3,171,091

TRANsFoRMER ENcAsED 1N MAGNETIC TAPE i,

Filed Aug. 2, 1960 INVENTOR .Piena/au M GozpsM/vw ATTORNEY United StatesPatent O 3,171,091 TRANSFORMER ENCASED 1N MAGNETIC TAPE Bernard M.Goldsmith, Little Silver, NJ., assignor to Nytronics, Inc.,Plrillipshurg, NJ., a corporation of New Jersey Filed Aug. 2, 1960, Ser.No. 46,920 14 Claims. (Cl. 336-83) This invention relates to electricalcoil and transformer constructions and is particularly useful inminiaturized applications.

It is an object of the invention to provide an improved construction ofthe character indicated.y

Another object is to provide, in a miniaturized coil or transformerconstruction, a maximum possible inductance per unit volume.

Another object is to meet the above objects with a constructionfeaturing a completely closed magnetic fluxconducting path to which aywinding is linked.

A still further object is to achieve the above objects in a constructionin which the possibility of `air gap development in any part of theflux-conducting path is reduced to zero.

A specific object is to achieve the above objects with a constructionthat lends itself to mass production with high reproducibility ofelectrical characteristics.

Other objects and various further features of novelty and invention willbe pointed out or will occur to those skilled in the art from a readingof the following specification in conjunction with the accompanyingdrawings. In said drawings, which show, for illustrative purposes only,preferred forms of 4the invention:

FIG. 1 is an enlarged view in longitudinal section of a coilconstruction embodying features of the invention;

FIG. 2 is a view similar to FIG. l but showing a modification;

FIG. 3 is a view similar to FIG. 1 but showing application of theinvention to a transformer;

FIG. 4 is an elevation of the transformer of FIG. 3, parts being shownin section in the plane 4 4 of FIG. 3; and

FIG. 5 is a simplified View similar to FIG. 3 but showing a modifiedtransformer construction.

Briefly stated, my invention contemplates application to miniaturizedcoil and transformer constructions Wherein a winding is developedgenerally centrally on an elongated cylindrical core of magneticflux-conducting material and wherein it is desired that theflux-conducting path toroidally envelop the winding without introducingany air gap in the magnetic-flux path. I have found that this can beachieved by applying high permeability tape or plastic as acircumferential envelopment of both the Wound and unwound exposedcylindrical parts of the core at both ends of the Winding, and byassuring that there is a residual compressed pressure contact of thehigh permeability plastic material on the unwrapped end parts of thecore. Various forms of the invention will be described.

In FIG. 1, the invention is shown in application to a simple single coilcomprising a plurality of closely adjacent turns of insulated wire onthe central part of an elongated cylindrical core 11 of magneticflux-conducting electrically insulating material. The core 11 may be aferrite, or it may comprise powdered iron bonded in a thermosettingplastic or resin, such as Teflon.

Lead elements 12-13 may be securely mounted at the respective ends ofthe core 11 which, for the core materials recited above, will beelectrically insulated. In the form shown, the lead elements 12-13 arecach received and bonded in a recess, as at 14, at an end of the core11; and to enhance the bond, the inserted end of the lead element may beupset as by nail-heading machinery ICC core 11 and a similar surface 18at the other end. The

respective ends of coil 10 may be brought out axially for wrapping andsoldering, as at 19 to the lead 12, and at 20 to the lead 13. Ifdesired, the core 11 may be provided with a longitudinal groove 21 tofacilitate alignment and retention of the respective coil'ends, whichare brought out for lead connection at 19-20.

In accordance with the invention, a continuous magnetic flux-conductingpath is completed utilizing high permeability magnetic flux-conductingtape which, in the form shown, is a single or helical circumferentialenvelopment or layer 22 surrounding both wound and unwound parts of thecore 11. To reduce to zero the possibility of air-gap development at thelocations 17-18 Where the flux path is closed, I provide for compressioncontact of the high permeability plastic layer 22 with these endsurfaces 17-18. In the form shown, such Contact is achieved byemployment of a sleeve 23 circumferentially stressed in tension and,thus, holding not only circumferential contact at 17-18 but also tightlyretaining the winding on the core.

The material of the sleeve 23 may be, in effect, a rubberband which isabnormally enlarged to receive insertion of the wound core and which is.allowed to compress with residual stress the remaining parts of theassembly. I prefer, however, to employ a sleeve 23 of irradiatedpolyethylene which goes by the trade name Thermofit,V being a product ofRaytherm Corporation of Redwood City, California. In employing thismaterial, it is initially supplied oversize, as suggested by thethickness dimension T in FIG. 1, the inner diameter being in excess ofthe outer diameter of the layer 22 prior to stressing. Such a sleeve 23is assembled in co-axial relation with the rest of the parts and is,finally, shrunk into placeby application of heat. The material noted hasthe property of shrinking to about 60 percent of its original size sothat if its size is initially selected to permit shrinkage only to, say,percent of its original size, then, to the extent that it has not beenable to shrink completely, a permanent residual circumferential tensionwill be established in the sleeve 23 upon shrinking, and this tensionwill apply constant radial pressure to the plastic layer 22, at least atthe desired points of firm contact, namely, at surfaces 17-18.

In a typical core construction of my invention, the

4core 11 is, as indicated, either of ferrite or bonded powdered iron. Itmay be of 0.070" diameter and 0.250" length. It is initially assembledwith the lead elements 12-13 which may be of #26 wire. The turns of thecoil 10 may be of #38 enameled magnetic wire, and the windingdevelopment may be a solenoid, universal, progressive universal, layerwound, bobbin wound, or insulated layer-wound type. The highpermeability plastic material of the layer 22 may be a thermoplasticmagnetic tape containing powdered iron in a suitable plastic vehicle,such as nylon, and I have found that satisfactory results may beachieved with that tape known as Ferrotron, being a product ofPolypenco, Inc., of Reading, Pennsylvania. Such tape comes in variouswidths and thicknesses and is applied in one or more turns of helicaldevelopment over the wound and unwound core 11 until the desiredthickness is achieved. In the illustrative example, such thickness inthe region of overlap with the single layer coil 10 shown may be such asto produce an outer diameter of layer 22 of 0.090.

Finally, shrunk sleeve 23. may be such Yas to produce a shrunk or nishedthickness of about 0.010"v benglprocured in the unshrunk form with, forexample, an inner diameter of 0.125" which would tend to shrink t 0.070"diameter butwhich, by virtue of the dimensions indicated above, will notbe permitted to shrink all the way, thus establishing the residualtension and assuring pressure contact to complete the magnetic circuit.

In the arrangement` of FIG. 2, they leads 12-13 are omitted and the ends25-26 of the winding 10 are loosely brought out. If desired, a smallcircumferential band 27 of adhesive tapemay be employed to bring thewindingl endsl or leads 25-26V toward each other. In View of thesimilarity of parts, the same reference numbers have been used in FIG.2.as in FIG. l, wherever applicable. In use, the coil of FIG. 2 may besupported intermedia-te the ends, as for example, by spring nger 28frictionally engaging the sleeve 23. at a central location.

FIG; 2V also servesto illustrate a circuit-element filter, featuringvery narrow band-pass characteristics when the core ofmaterial. 11 is' amagnetostiictive material as, for example, a magnetostrictive ferritewhich has been initially magnetically polarized.v In such applications,the inductance presented; tothe leads 25-26 will be sharply dependentupon the mechanical-resonance characteristics of the core 11 (inthelongitudinal direction) and, if desired,a1se`cond;winding (not shown)may be wound adjacent to or over the winding 10 toy provide independentinput and output circuits, that is, circuits which are electricallyindependent but whose coupling depends solelyuponA theVmechanical-resonance characteristics of the core 11.

In FIGS. 3 and 4, I illustrate' application of the invention. to atransformer construction in which the primary andsecondary windingsyltland 10 are developed on separate cores 11411 of generally the sameshape but. ar-

rangediin side-byLside relation, there-being a spacer 30' of?electrically insulating material preferred between adjacent parts of thewinding 1040'. For convenience in description, the upper coil andcore10-11may be similar to-that described in FIG. l, and corresponding partsof the lower coiland core 10'11' are, therefore, given thev same.reference numbers, but withy primed notation. It willibe noted that thecoil 10' is amultilayer coil carried by the core 11'. Leads to the rstcoil 10` are brought out at 12-13, and thoseto the second coil-10are'brought outiat 12-13. For transformer action, it isfnecessarythat'the core 11 and the core 11 shall be part of one and the samecontinuous ux path, and tol achieve this, in accordance with theinvention, I cause the wrap22 of'high permeability material to bebandedto-and thus to overlapand'envelopfboth coils and 4both cores, as will beseen moreclearly inthe vie'wy of FIG.' 4.

This means, then, that the fluxV path" maybe considered to follow thearrows of FIG. 3 as, for'example, from left to right in the bodyk ofcore 11, thence dividing Vin parallel arms defined by stretches 32-33 ofthe high permeability materialv 22 at the right-hand end of the assemblyof FIG. 3; from these points (stretches 32-33), the ux re-enters thecore 11 and proceeds from right to left, for division into two parallelbranches again in stretches 324335at the left hand of FIG. 3, and nally,re-enters the core 11.l In the form of FIG. 3, the use of tape 22 toenvelop the coils as well as the unwound parts of the cores, means thatthe remaining parts -of the tape 22y will serve to shield the coils10-10 against strayfluxes. The assembly is completed by employment of acompression sleeve 23', `such as described at 23 for FIG. 1 and,preferably, shrunk into stressed compressional contactgwith unwoundextensive areas at the ends of both cores 11-11.

The arrangement of FIG. is simplified and somewhat schematic but servesto illustrate a modification of FIG. 3 in which separate tapes 35-36 areseparately banded to corresponding ends of coresY 11-11; tapes 3S-36'thus complete -the ux path at the ends of the cores 11-11. Separatecompressional sleeves may be applied over the tapes 35-36, but Iindicate my preference that a single such sleeve 37 be employed tooverlap both the tapes 35-36 and the windings 10-10.

It will be seen that I have described improved coil and transformerconstructions featuring maximum inductance per unit volume. This resultis achieved primarily by reducing air-gap development to zero and, thus,assuring continuous magnetic linx-path development. The constructionlends itself to single layer, multi-layer and various other windingforms, and it may be easily fabrica-ted with great precision andreproducibility of electrical characteristics. or 357 may provide atough protecting hide for the overall assembly.

While the foregoing description sets forth the principles of theinvention in connection with specific apparatus, it is to be understoodthat this description is made only by way of example and not as alimita-tion of the scope of the invention as defined in the accompanyingclaims.

I claim:

1. An electrical coil construction, comprising an elongated cylindricalcore of magnetic-flux conducting material, a winding including pluralityof turns over a portion of said core short of the axial ends thereof,there being thus exposed a substantially continuous cylindrical coresurfacev at each end of said winding, and magneticflux conducting meansconnecting said surfacesk independent of linkage to said winding, saidlast-delined means including plastic tape means of high-permeabilitymaterial and circumferentially extending means radially inwardlycompressing the high-permeability material into pressure contact witheach of said end surfaces.

2. A construction according to claim 1, in which said tape meanscompletely envelops said coil and is in pressurecontactfwithv saidsurfaces at the ends of said core.

3. A construction according to claim 1, and including a second elongatedcylindrical core of magnetic flux-conducting material, a` second windingincluding turns carried by a portion of said second core intermediatethe axial'ends thereof, whereby cylindrical end surfaces areexposedatboth ends of said second winding, said'tape means including afirst portion of high-permeability material banded in-pressure con-tactwith a first end surface of the first core and with a rst end surface ofthe second core, said 'tape means including a second portion ofhighpermeability material banded in pressure contact with both theopposi-te end surfaces of said cores.`

4. A transformer comprising two elongated cylindrical cores of magneticflux-conducting material, separate windings including first turnscarried intermediate the ends of a first core and second turns carriedintermediate theends of the second core, said wound cores being dis'-posed side-by-side and having corresponding exposed cylindrical coresurfaces at the respective ends of each of said windings, and tape meansof high permeability material includinga irst portion banded in pressureContact with" iii-'st corresponding adjacent end surfaces of said coresand a second portion banded in pressure contact with correspondingadjacent opposite end surfaces of said cores.

5. A transformer according to claim 4, and including a spacer ofinsulating material intermediate adjacent parts of the respectivewindings.

6. A transformer according to claim 4, in which said separate portionsof tape are separate ltapes in pressure contact only withend surfaces ofsaid cores.

7. A transformer according to claim 4, in which said tape means envelopsboth the unwound and wound portions of said cores and is in pressureContact with said cores at the end surfaces thereof.

8. A coil construction comprising an elongated cylindricalcore ofmagnetic flux-conducting material, an electrical winding including aplurality of turns developed on Once assembled, the outer sleeve 23 or23` the core intermediate the axial ends thereof, whereby substantiallycircumferentially continuous cylindrical end surfaces of said core areexposed at both ends of said winding, and a tape of high permeabilitymaterial continuously enveloping both the wound and unwound cylindricalportions of said core and circumferentially extending means radiallyinwardly compressing the highpermeability material into pressure Contactwith said unwound portions.

9. A coil construction comprising an elongated cylindrical core ofmagnetic flux-conducting material, an electrical winding including aplurality of turns developed on the core intermediate the axial endsthereof, whereby substantially circumferentially continuous cylindricalend surfaces of said core are exposed at both ends of said winding, atape of high permeability material continuously enveloping both thewound and unwound cylindrical portions of said core and in pressurecontac-t with said unwound portions, and a sleeve of plastic materialcircumferentially enveloping said high permeability material in residualcircumferential tension, whereby pressure Contact of said highlypermeable material with the unwound cylindrical core ends is achieved.

10. A coil construction comprising an elongated core of magneticflux-conducting electrically insulating material, leads carried at therespective ends of said core in electrically insulated relation witheach other, an electrical Winding of insulated wire having turnsdeveloped on said core in closely adjacent relation to each other, saidwinding extending short of the axial ends of said core, wherebysubstantially circumferentially continuous surfaces of the core areexposed at both ends of said winding, the free ends of said windingbeing connected respectively to said leads, a layer of high permeabilitymagnetic Eux-conducting plastic completely surrounding both wound andunwound cylindrical portions of said core, and a compression sleevesurrounding said ilux-conducting plastic and in intimate tensed contacttherewith, whereby extensive pressure contact of said flux-conductingplastic with both unwound ends of said core is achieved.

11. Coil construction comprising an elongated core of magneticflux-conducting electrically insulating material, an electrical windingof insulated wire having turns developed on said core in closelyadjacent relation to each other, said winding extending short of theaxial ends of said core, whereby substantially circumferentiallycontinuous surfaces of the core are exposed at both ends of saidwinding, a layer of high permeability magnetic uxconducting plasticcompletely surrounding both wound and unwound cylindrical portions ofsaid core, and a compression sleeve surrounding said flux-conductingplastic and in intimate tensed contact therewith, whereby extensivepressure contact of said ilux-conducting plastic with both unwound endsof said core is achieved.

l2. A device according to claim 11, in which said core is ofmagnetostrictive material.

13. A device according to claim 12, and including supporting meansintermediate the axial ends of said core and supporting the assembly bycontact with said sleeve.

14. A transformer including two elongated cylindrical cores of magneticilux-conducting material, a separate winding on each of said cores, saidwound cores being disposed side-byside with the corresponding endsthereof adjacent one another, and tape means of high permeabilitymaterial including a first portion banded in pressure contact with rstcorresponding adjacent ends of said cores and a second portion banded inpressure contact with second corresponding adjacent ends of said cores.

References Cited in the file of this patent UNlTED STATES PATENTS352,105 Zepernowsky Nov. 2, 1886 1,994,534 Robinson Mar. 19, 19352,457,806 Grippa lan. 4, 1949 2,79 1,753 Jeppson May 7, 1957 2,938,210Harris May 24, 1960 2,966,704 OBrian et al. Ian. 3, 1961

1. AN ELECTRICAL COIL CONSTRUCTION, COMPRISING AN ELONGATED CYLINDRICALCORE OF MAGNETIC-FLUX CONDUCTING MATERIAL, A WINDING INCLUDING PLURALITYOF TURNS OVER A PORTION OF SAID CORE SHORT OF THE AXIAL ENDS THEREOF,THERE BEING THUS EXPOSED A SUBSTANTIALLY CONTINUOUS CYLINDRICAL CORESURFACE AT EACH END OF SAID WINDING, AND MAGNETICFLUX CONDUCTING MEANSCONNECTING SAID SURFACES INDEPENDENT OF LINKAGE TO SAID WINDING, SAIDLAST-DEFINED MEANS INCLUDING PLASTIC TAPE MEANS OF HIGH-PERMEABILITYMATERIAL AND CIRCUMFERENTIALLY EXTENDING MEANS RADIALLY INWARDLYCOMPRESSING THE HIGH-PERMEABILITY MATERIAL INTO PRESSURE CONTACT WITHEACH OF SAID END SURFACES.